The Cortana taskbar disappeared from the screen, how can I get it back?

Right-click on the Taskbar at the bottom of the screen and look at the context menu until you find Cortana. Hover over the Cortana option until you see three options:
Hidden
Show Cortana icon
Show search box

Hidden should have a checkmark next to it. If you want just a little icon then select that one, and the third option is the full Cortana search bar.